Problem: Simplify the following expression: ${3(7-y)-3(-3y+5)}$
Solution: Distribute the ${3}$ into the first set of parentheses: $ {3(}\gray{7-y}{)} - 3(-3y+5) $ $ {21-3y} - 3(-3y+5) $ Distribute the ${-3}$ into the parentheses: $ 21-3y {-3(}\gray{-3y+5}{)} $ $ 21-3y + {9y-15} $ Rewrite the expression to group the ${y}$ terms and numeric terms: $ {-3y + 9y} + {21 - 15}$ Combine the ${y}$ terms: $ {6y} + {21 - 15}$ Combine the numeric terms: $ {6y} + {6}$ The simplified expression is $6y+6$